Trouble removal of hydraulic system on the QY8 truck crane (1)

In the process of using a QY8 truck crane, the hydraulic pressure of the hydraulic system is low. When operating the variable amplitude handle to make the variable cylinder shrink to the bottom, the pressure gauge shows only 12MPa, and when increasing the throttle, the pressure is only 16MPa (the relief valve is set at 21MPa). The working principle of the hydraulic system of this machine is shown in Figure 1. The reasons for its low pressure may be analyzed in 5 aspects:

(1) the oil filter 2 is blocked. If the oil filter filter surface is attached to a layer of sludge, then the plunger pump 1 will produce suction phenomenon, so that the oil pressure is too low.

(2) the piston pump is too big to leak in 1. If the piston and cylinder bore wear the clearance is too large, or because of damage between the valve plate and cylinder pull have grooves, will cause the plunger pump discharge is too large.

(3) the control valve 7 is too large. If the gap between the valve stem and the valve body is too large, the valve will leak and the hydraulic fluid will flow directly to the tank 9.

(4) the overflow valve on the train has 6 trouble. If the setting pressure of the valve is too low, or the contact between the poppet valve and the valve seat is bad, the system pressure is too low.

(5) discharge valve 3 is too large. When the operation is on the bus, the branch valve is pulled out and the leg control valve is placed in the middle, the hydraulic oil will flow back to the tank directly through the leg control valve, and the system pressure is too low because of the large leakage in the shunt valve.